Rosemary Shrub Care: Sun, Drainage and Winter Protection

Rosemary is an evergreen woody shrub that wants full sun, light well-drained soil and a dry root zone, and it is reliably hardy only in about USDA zones 8 to 10. Penn State describes it as an aromatic shrub with needle-like leaves, growing 2 to 6 feet tall. Colder gardens can still grow it in a pot and bring it indoors. The ASPCA lists rosemary as non-toxic to dogs, cats and horses. This guide treats rosemary as an ornamental shrub for borders, hedges and containers; its plant name is Salvia rosmarinus at NC State, and Rosmarinus officinalis at UMD Extension.

USDA zones

8–10 (Penn State); a few cultivars to zone 6b–7 with protection

Sun

Full sun, at least 6 hours

Water

Drought tolerant once established

Origin

Mediterranean

Container friendly

Yes

Soil

Light, well drained; not clay

Size

2–6 ft tall and wide (Penn State)

Bloom time

Spring into summer

Pets

Non-toxic to dogs, cats and horses (ASPCA)

Zones and winter

Penn State gives USDA zones 8 to 10. Illinois Extension says rosemary is not reliably hardy in zone 6 or colder, and that in the Midwest it often does not overwinter and is best treated as a tender perennial and brought indoors for the winter. UMD Extension also describes it as tender in the Northeast and Midwest.

Penn State lists hardier cultivars: ‘Arp’, ‘Athens Blue Spire’, ‘Madalene Hill’ and ‘Miss Jessop’s Upright’ tolerate zone 7, or zone 6b with protection. Choose among these if you garden at the cold edge and want to keep a rosemary in the ground.

Sun and light indoors

NC State lists full sun. Penn State says most herbs need 6 hours of direct sunlight, and that herbs grown indoors need a sunny window or grow lights to get it.

Soil and water

NC State says rosemary grows in light, slightly acidic, dry to medium, well-drained soil and tolerates most soil types except clay. UMD Extension gives a different pH: it says rosemary grows best in well-drained soil with a pH of 6.5 to 7.0. Both agree on drainage. NC State says it tolerates drought, partial shade, salt, heavy pruning and most soil types except clay, and that overwatering and wet, humid conditions are the main risk.

Size and use

Penn State says 2 to 6 feet tall and 2 to 6 feet wide, NC State says 4 to 5 feet tall, erect and rounded, and UMD Extension says 36 to 72 inches. Penn State separates two habits.

Planting and containers

Illinois Extension says rosemary plants grown in the garden do not transplant very well, so plant in a container if you will be moving it indoors for winter. That also suits the prostrate types Penn State recommends for pots and hanging baskets.

1. Choose full sun and light soil. At least 6 hours of direct sun (Penn State), in well-drained soil that is not clay (NC State).
2. Decide: ground or pot. In zone 8 to 10 the ground is fine; colder gardens are better with a container (Illinois Extension).
3. Water to avoid wet feet. Overwatering and humid, wet conditions are the main risk (NC State).
4. Bring pots in before cold arrives. Move to a protected spot or indoors for winter (UMD Extension, Illinois Extension).

Feeding and pruning

Illinois Extension says to fertilize regularly for the best foliage. NC State says severe pruning after bloom encourages dense growth, and UMD Extension says to pinch seedlings and young plants to direct growth. Our rosemary pruning guide covers timing, how much to take and why bare woody stems should not be cut.

Flowers

NC State says rosemary blooms from spring into summer, with small white, pink, blue or lavender flowers that draw pollinators. Illinois Extension says that during the summer it produces small white, pink or blue flowers. For the plants it sits beside in the garden, our bloom calendar shows how long each one flowers.

Propagation

Illinois Extension says stem cuttings are the most reliable way to propagate rosemary, because seed is slow to germinate. NC State adds that layering or division also work.

Grow these next

Rosemary shares its need for sun and drainage with the lavender guide, another shrub that dislikes wet roots. For a heat-loving shrub that grows much larger, read the oleander guide, which carries a pet-toxicity warning, unlike rosemary.